return standardLowerEntry(key);
    }

    @Override
    public @Nullable K lowerKey(K key) {
      return standardLowerKey(key);
    }

    @Override
    public @Nullable Entry<K, V> floorEntry(K key) {
      return standardFloorEntry(key);
    }

    @Override
    public @Nullable K floorKey(K key) {
      return standardFloorKey(key);
    }

    @Override

    public @Nullable K lowerKey(@ParametricNullness K key) {
      return sortedMap().lowerKey(key);
    }

    @Override
    public @Nullable Entry<K, Collection<V>> floorEntry(@ParametricNullness K key) {
      Entry<K, Collection<V>> entry = sortedMap().floorEntry(key);
      return (entry == null) ? null : wrapEntry(entry);
    }

    @Override
    public @Nullable K floorKey(@ParametricNullness K key) {

    public @Nullable Entry<K, V2> firstEntry() {
      return transformEntry(fromMap().firstEntry());
    }

    @Override
    public @Nullable Entry<K, V2> floorEntry(@ParametricNullness K key) {
      return transformEntry(fromMap().floorEntry(key));
    }

    @Override
    public @Nullable K floorKey(@ParametricNullness K key) {
      return fromMap().floorKey(key);
    }

    @Override

    public @Nullable Entry<K, V2> firstEntry() {
      return transformEntry(fromMap().firstEntry());
    }

    @Override
    public @Nullable Entry<K, V2> floorEntry(@ParametricNullness K key) {
      return transformEntry(fromMap().floorEntry(key));
    }

    @Override
    public @Nullable K floorKey(@ParametricNullness K key) {
      return fromMap().floorKey(key);
    }

    @Override

        return nullableSynchronizedEntry(delegate().firstEntry(), mutex);
      }
    }

    @Override
    public Map.@Nullable Entry<K, V> floorEntry(K key) {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().floorEntry(key), mutex);
      }
    }

    @Override
    public @Nullable K floorKey(K key) {
      synchronized (mutex) {

        return nullableSynchronizedEntry(delegate().firstEntry(), mutex);
      }
    }

    @Override
    public Map.@Nullable Entry<K, V> floorEntry(K key) {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().floorEntry(key), mutex);
      }
    }

    @Override
    public @Nullable K floorKey(K key) {
      synchronized (mutex) {

  public @Nullable K lowerKey(K key) {
    return keyOrNull(lowerEntry(key));
  }

  @Override
  public @Nullable Entry<K, V> floorEntry(K key) {
    return headMap(key, true).lastEntry();
  }

  @Override
  public @Nullable K floorKey(K key) {
    return keyOrNull(floorEntry(key));
  }

  @Override
  public @Nullable Entry<K, V> ceilingEntry(K key) {
    return tailMap(key, true).firstEntry();

    }
    {
      Entry<Integer, String> entry = unmod.lowerEntry(1);
      assertThat(entry).isNull();
    }
    {
      Entry<Integer, String> entry = unmod.floorEntry(2);
      assertThrows(UnsupportedOperationException.class, () -> entry.setValue("four"));
    }
    {
      Entry<Integer, String> entry = unmod.ceilingEntry(2);

    }
    {
      Entry<Integer, String> entry = unmod.lowerEntry(1);
      assertThat(entry).isNull();
    }
    {
      Entry<Integer, String> entry = unmod.floorEntry(2);
      assertThrows(UnsupportedOperationException.class, () -> entry.setValue("four"));
    }
    {
      Entry<Integer, String> entry = unmod.ceilingEntry(2);